Category slugs assignment is not user friendly.

[vi]

Problem

package.categories field in Cargo.toml is hard to get right on the first attempt.

Steps

1. Start a new project: cargo new --lib somelib
2. Do the code
3. Fill in license, README and discoverability-related Cargo.toml fields
4. cargo publish --dry-run
5. cargo publish. warning: the following are not valid category slugs and were ignored: testing.
6. Be annoyed that the flawed version got published, but it's too petty to yank or bump-and-reupload; so the discoverability penalty of not having the category will persist for long (because of subsequent versions of this mini-library may never be needed).
7. Check the resulting crates.io page and discover that readme = "README.md" is also missed.

Possible Solution(s)

• More comments in template Cargo.toml for libraries. In particular, https://crates.io/category_slugs link is hard to find. You need to fail the quest to get it from the "game over screen" (cargo warning that crate is published, but category ignored).
• Error instead of warning if category is wrong
• Real --dry-run. Actually connecting to crates.io and checking for all possible obstacles.
• Maybe just including the entire list in https://doc.rust-lang.org/cargo/reference/manifest.html instead of just linking it. Or at least making crates.io/category_slugs part an actual, clickable link there.

Notes

Output of cargo version:

cargo 1.37.0-nightly (545f35425 2019-05-23)

[ehuss]

It was decided in #6881 to keep the new template to just the minimal basics, with a comment pointing to the documentation.

There is a desire to enhance the publish API to support things like dry-run. See rust-lang/crates.io#1522.

I don't know why invalid categories are warnings instead of errors. You'll need to file an issue on /~https://github.com/rust-lang/crates.io/issues.

[ehuss]

I'm going to close this for now as the requested enhancements already have issues or are already well known, or not something in Cargo's control. We would definitely like to make the publishing process smoother, though!